[volt-nuts] Thermistor value for 732A Reference 10V Standard

[Mitch Van Ochten]

Hi Tom,

According to the Fluke 732A manual page 2-6 the nominal value is between 
3k - 4k with the oven at normal operating temperature.  Mine checks 3.545 k 
and has been within a few ohms of that reading each year for five years. You 
may have a heater problem.  There is a protective thermal fuse which can go 
open, in series with the heating elements.  It's purpose is to prevent a 
runaway oven from cooking everything.  Once it opens you will never get any 
heating until it is replaced.


Regards,

mitch



----- Original Message ----- 
From: <Leedyt at aol.com>
To: <volt-nuts at febo.com>
Sent: Thursday, June 28, 2012 7:04 PM
Subject: [volt-nuts] Thermistor value for 732A Reference 10V Standard


>
>
> Hi!
>
> Can anyone give me a rough value of the thermistor resistance that is
> brought out to the front panel of a Fluke 732A DC Reference Standard 
> (lower
> left-hand side)?  The thermistor is for the user to monitor the 
> temperature  of
> the oven that contains the voltage reference.  I see a resistance that
> starts out at 6600 Ohms (unit was nearly cold) and climbs and levels out 
> at
> about 8400 Ohms after a day, or so.  Is this reasonable?  The  thermistor 
> is
> given in the parts list as RT2, a Fenwal JA41J1 (no longer made)  and on 
> the
> schematic as a 10K @ 25C unit.  So this doesn't make  sense.
>
> Does anyone have any experience with this?  Or is just simpler to  replace
> the thermistor with a 100 Ohm RTD and be done with it?  Or would  this 
> drive
> the calibration labs nuts?
>
> Any references or advice would be appreciated.
>
> Tom Leedy
> Clarksburg, MD
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